The proteins responsible for the exchange of Cl- with HCO3- are members of the SLC4 (1-3) and SLC26 (3, 4, 6, 7 and 9) transporter families. SLC4A1 (Band 3, AE1, anion exchanger 1) was the first bicarbonate transporter gene to be cloned and sequenced. It is ubiquitous throughout vertebrates and in humans, is the major glycoprotein present on erythrocytes and the basolateral surfaces of kidney cells. Variations in erythroid SLC4A1 determine the Diego blood group system. Mutations in the erythrocyte form of SLC4A1 can cause hereditary spherocytosis type 4 (HSP4; MIM:612653), a disorder leading to haemolytic anaemia (HA). Some mutations in SLC4A1 can cause distal (type1) renal tubular acidosis (dRTA; MIM:179800) (an inability to acidify urine) and dRTA-HA (dRTA with hemolytic anemia) (MIM:611590) (Tanner 2002, Romero et al. 2013).